diff --git a/src/router/UnknownRouterException.php b/src/router/UnknownRouterException.php
index 5282e22..73f2081 100644
--- a/src/router/UnknownRouterException.php
+++ b/src/router/UnknownRouterException.php
@@ -11,13 +11,13 @@
 namespace Facebook\HackRouter;
 
 class UnknownRouterException extends InternalServerErrorException {
-  public function __construct(private array<mixed> $fastRouteData) {
+  public function __construct(private varray<mixed> $fastRouteData) {
     parent::__construct(
       'Unknown FastRoute response: '.\var_export($fastRouteData, true),
     );
   }
 
-  public function getFastRouteData(): array<mixed> {
+  public function getFastRouteData(): varray<mixed> {
     return $this->fastRouteData;
   }
 }